Receiver for ultra high frequency waves



Feb. 14, 1939. l R p BRADEN 2,147,142

RECEIVER FOR- ULTRA HIGH FREQUENCY WAVES Filed 'July 14, 1936 I 2 Sheets-Sheet l k x Q an i a x I, I Q

MPL/Ha' Illinw Q Q V IMIHII Snventor Feb.` 14, 1939.

` R. A. BRADEN RECEIVER FOR ULTRA HIGH FREQUENCY WAVES 2 Sheets-Sheet 2 Filed July 14, 1936 EGLI Bf QM Gttomeg Cil Patented Feb. 14, 1939 UNITED STATES PATENT OFFICE RECEIVER FOR ULTRA HIGH FREQUENCY WAVES Rene A. Braden, Collingswood, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application July 14,

2 Claims.

currents of relatively low frequency which may be created by sixty cycle induction, electrical switching, lightning. discharges, automobile ignition, and the like. My invention contemplates means for eliminating or reducing such disturbing effects Without attenuating the desired ultra short wave currents.

One of the objects of my invention is to provide means for shielding an ultra short wave antenna from low frequency disturbances. Another object is to provide an ultra high frequency antenna with shielding means which permit waves of predetermined polarization to reach the antenna. A further object is the provision of means for shielding the transmission line of an antenna system from low frequency disturbances and by providing means for attenuating low frequency disturbances in the transmission line.

My invention may be best understood by reference to the accompanying drawings, in which Fig. 1 represents an ultra short wave receiving system with an unshielded antenna and trans- In a conventional ultra short wave receiving I system, such as disclosed in Fig. 1, a magnetron detector I may be enclosed within a shield 3. The magnetron is connected to a transmission line 5 which terminates in a dipole antenna l. The midpoint of the dipole is connected through 1936, Serial No. 90,456

(Cl. Z50-20) a radio frequency choke 9 to an audio amplifier II. The radio frequency choke is also connected to an audio frequency inductor I3 and a power supply I5 which energizes the magnetron anode circuit.

The audio amplifier II, choke 9, in-

ductor I3, and power supply I5 are preferably .shielded by a container I'l.

The output of the audio amplifier may be connected to any sultable signal indicator.

The magnetron detector is a high impedance vdeviceA andin th system shown is particularly sensitive to low frequencyv disturbances which may reach the antenna or' transmission line.

One arrangement for shielding the antenna system from low frequency currents without attenuating the desired ultra high frequency currents, is shown in Fig. 2. In this figure, and

throughout the specification and drawings, similar reference numerals willbe used to indicate similar parts.

The dipole antenna l is located amplifier II and power source The grounded cage shields the I5, is shielded. antenna from low frequency disturbance but admits ultra high frequency currents which are polarized in the plane of the dipole antenna 1.

In Figs. 3 and 4, the detector 25 is connected by a suitable transmission line 5 tenna 1.

to a dipole an- The detector and transmission line are suitably shielded. The dipole 'I is positioned at the focus of a reector 21 which also acts as a shield. A series of conductors 29 are connected across the opening of the reflector.

The conductors are preferably arranged substantially at right angles to the axis of the dipole and are uniformly spaced with respect to each other.

frequency.

so that it may be tuned to currents of signal The reector and dipole must beA suitably arranged with respect to the approaching wave front in accordance with the well known directive effect of a dipole and reector.

The directive effect is a further aid in reducing disturbances originating behind the reflector.

In Fig. a magnetron I or any other detector, such as a positive grid triode, is connected to a transmission line 3l which terminates in a dipole antenna 1. The dipole antenna is located at the focus of a reflector 21. The magnetron and transmission line are positioned .Within a shield 33. A pair of capacitors 35 are serially included in the transmission line 5. These capacitors 35 may be small discs which are suitably spaced so that they offer high reactance to low .frequency currents and negligible reactance to the ultra high frequency currents. The lengths of the transmission lines must be 'adjustable to allow tuning the lines to the wave length of the received signal, and to permit placing the capacitors 35 at or near a Voltage or current.- node, so that the reflections from the capacitors will be in step with those from the ends of the line. lIn this manner, the disturbing low frequency currents are highly attenuated, while the desired high frequency currents are not appreciably attenuated. The antenna 1 and its reector 21 may be replaced by any suitable antenna array.

In Fig. 6, a magnetron detector I is connected to a transmission line 31. The transmission line 31 is terminated in a loop .39. The detector, transmission line, and loop are located within a shield 4|. The line 31 is preferably tuned to currents of signal frequency. 'Ihe portion of the shield which is near the loop 39 is arranged to permit magnetic coupling to the loop, butthis portion of the shield excludes capacity coupling. A -second loop 43 is inductively coupled to .the rst mentioned loop 39. The second loop pedance.

is part of a. second transmission line 45. A dipole antenna 41 is connected to the second transmission line 45 at points at which the antenna impedance is suitably related to the line im- 'I'he transmission line 45 is tuned by an adjustable bridge member'49 which may be a trombonef or the like. In this arrangement, the inductive relation between the loops 39, 43 oiers relatively low impedance to desired high frequency currents and very high attenuation to undesired low frequency disturbances. The magnetron and its associated transmission line is electrostatically shielded from low frequency currents, but is exposed to the desired high frequency currents through the inductive coupling between the loops of the transmission lines.

I'hus I have described an ultra high frequency A frequecy'waves.

detector which is connected to a transmission line. A dipole is connected or coupled to the transmission line. The transmission line, detector, and dipole may be shielded with respect to low frequency disturbances, the detector is connected to the terminating end of the transmission line. The dipole is shown as shielded by conductors which exclude low frequency disturbapnces but admit properly polarized ultra high Couplings of high impedance to the W frequency disturbances may be included in the transmission line. Although parallel wire transmission lines have been shown, it shown be understood that concentric shielded lines may be used. Likewise, equivalents may radio frequency detectors, such as a positive grid tube, may be used in place of the magnetron detectors. The shielded antenna system of my invention may be used on a transmitting system to prevent undesired low frequency currents from modulating the transmitter.

I claim as my invention:

1. In an ultra high frequency system, the combination of a detector, an antenna, a transmission line connecting said antenna and terminating in said detector, means shielding said detector and transmission line from disturbing low frequency currents, and reactive means between said antenna and said detector for attenuating low frequency currents without appreciably attenuating ultra high frequency currents, said last named means being placed at points in said transmission line which substantially insure that the reflections from said last named means and the reflections from the termination of said line will be in step.

2. In an ultra high frequency system, the combination of a detector, an antenna, a transmission line connecting said antenna and terminating in said detector, means shielding said detector and transmission line from disturbing low frequency currents, and capacitors connected in said transmission line whereby the reactance to low frequency currents is high with respect to the reactance to desired ultra high frequency currents, said capacitors being placed at points in said transmission line which substantially insure that the reflections from the capacitors and the reflections from the termination of the line will be in step.

RENE A. BRADEN. 

